1. Field of the Invention
The present invention relates to capacitive sensing circuitry for use with indicating differential pressure sensed by two sensor portions which are fluid filled and in fluid communication with each other.
2. Description of the Prior Art
In the prior art various capacitive sensing circuits have been advanced. Further, various sensors have been advanced for sensing differential pressure in response to deflections of separate diaphragms where a deflection in one direction of one of the diaphragms will cause an opposite deflection of another diaphragm because of a substantially incompressible fluid transferring the diaphragm motions to each other. For example, U.S. Pat. No. 4,398,194 shows such a sensor.
This device shows fairly flexible diaphragms mounted on opposite ends of a single block, and a circuitry for correcting span errors induced by changes in the density of the filling fluid as a function of temperature changes. This device, however, requires that the diaphragms be closely matched in stiffness in order to minimize zero errors induced by changes in fill fluid density.
Many circuits for providing the necessary output signals incorporate complex temperature compensating circuits that require costly temperature cycling and adjustment procedures. The problems of providing a simplified circuit which compensates for both zero and span errors without costly temperature cycling have limited usages of the oil filled, double diaphragm differential pressure sensors. The present invention teaches the solution to such problem when using double diaphragm capacitive sensors in which the diaphragm to capacitor plate spacing is substantially zero before oil filling.